Digital watermarking of 3D geometric model for rapid prototyping system

In this paper, a new watermarking algorithm for STL files which contain 3D geometric information as triangular facets is proposed. STL file format is widely used in CAD and rapid prototyping industry as a standard interchange format. The proposed algorithm embeds multi-bit watermark information into the surface normal vector and vertex description area of triangles of STL files without distorting the original 3D geometric shape. According to the embedded watermark bits, the starting position of normal vector and the direction of vertex sequence of the triangles are modified. The proposed algorithm is robust against simple attacks like changing the order of the triangular meshes. In addition, the invisibility requirement is also satisfied. Experiment results show that the proposed algorithm can encode and decode watermark bits into the various STL files without any distortion of 3D shape.